1. Field of the Invention
This invention relates to reducing the caking tendency of nitrogenous, or nitrogen-containing, materials. More particularly, it relates to a method and composition effecting a free flowing nitrogen-containing material that can be prepared in a composition that will yield the desired percent by weight nitrogen analysis. In specific aspects, this invention relates respectively to: (1) production of treated, non-caking nitrogen-containing salts, such as ammonium nitrate; these treated salts being valuable as free flowing fertilizer with little or no tendency to cake on standing; (2) nitrogen-containing salts, such as ammonium nitrate, treated to reduce their normal tendency to cake on standing and to explosive compositions containing such treated salts; and (3) novel two-component anti-caking agents, useful in treating such salts and to a method of preparing such anti-caking agents.
2. Description of the Prior Art
Maintenance of a free flowing nitrogen-containing material in its manufactured form, either crystalline, granular or pellets, under long term storage conditions, has long been a problem in the art. The term "particles" will be employed herein in its broad sense to include all of these forms of the nitrogen-containing material. Most of the nitrogen-containing salts or materials have a normal tendency to cake or become sticky on standing and form hard masses, regardless of the form in which they are manufactured. This caking is usually promoted by changes in humidity, temperature and/or pressure and occurs under conditions during storing, shipping and handling.
The tendency of these salts to cake on standing presents difficulties in handling and use of such salts. For example, where such nitrogen-containing salts are used as fertilizers, this caking tendency impairs the durability of the fertilizer, increases the effort and cost of uniformly distributing the fertilizer in the field because caked fertilizer causes clogging of distribution machinery and other handling problems. Similarly, where nitrogen-containing salts, such as ammonium nitrate, are used as ingredients in explosive compositions, the caking tendency of such salts adversely affects the sensitivity of the explosive composition and may render it incapable of satisfactory detonation.
Many methods have been proposed in the past for overcoming, reducing or preventing the normal tendency of such nitrogen-containing materials to cake on standing. This problem of reducing the caking tendency, or imparting the anti-caking property, is worsened where the nitrogen-containing material has to meet a particular percent nitrogen analysis such that the amount of additive is limited if the nitrogen-containing material is to meet specifications. For example, it is known that urea must have a particular minimum percent nitrogen on analysis, such as about 45 percent and, preferably, 46 percent. A large number of excellent discussions of the problem are contained in the literature and U.S. patents. Typical of the art directed at, for example, urea is CHEM TECH, "Urea Technology -- a Critical Review," A. V. Slack and G. M. Blouin, January 1971, pages 32-40; and U.S. Pat. Nos. 3,112,343; 3,123,637; and 3,535,376. A review of the patent art alone indicates that a wide variety of methods and agents have been employed in attempting to prevent caking of nitrogen-containing materials. For example, the patents have shown the following materials, as illustrative of the classes of materials which have been employed heretofore: (1) ammonia; (2) magnesium carbonate; (3) film of metal resinate and gelled hydrocarbon; (4) basic aluminum sulfate; (5) substituted urea, added during manufacture or to the finished prills; (6) a variety of heat treatments; (7) urea-formaldehyde condensation product in homogeneous composition of matter; (8 ) kaolin and alkali metal salts of alkyl arylsulfonic acids; (9) aliphatic amines; (10) sugar; (11) amine treated clays where the amine is a primary n-aliphatic mono amine containing 8-22 carbon atoms and preferably employing an oily solvent for the amine, an oily solvent being a hydrocarbon or a fatty acid nitrile containing 18-22 carbon atoms; (12) urea coated with a thin layer of a condensate of urea reacted with a vapor of a lower aldehyde or ketone in a uniform admixture of the vapor and urea at a temperature greater than 50.degree. C. and less than the melting point of urea; (13) lower carboxylic acid amides; (14) dispersions of paraffin waxes and urea overlaid with wax-urea adducts; and (15) respective screening and heating to optimize the size; for example, particles passing through 8 and not through a number 40 screen size; and moisture content; for example, 0.3-0.8 percent by weight. Some of these additives, or methods, were elaborate and expensive but were at least partially successful; while others were relatively unsuccessful. Similarly, other patents, such as U.S. Pat. No. 3,116,185 have reported on a wide variety of different additives and methods attempting to impart anti-caking property.
The closest art of which I am aware is U.S. Pat. No. 3,660,070. That patent describes a much more complicated process than this invention and effects a much more complicated composition of matter. Therein, an aqueous solution of alkyl sulfates, alpha-olefin sulfonates or alkyl sulfonates containing 6-10 carbon atoms are employed as a solubilizer to dissolve in aqueous solution water insoluble polymers; and the resulting aqueous solution is interacted with the fertilizers. The resulting fertilizer forms a hard cake that has to be reground. Thus, this complicated process is not totally satisfactory for a simple, economical solution as desired.
Despite the urgent problem, as attested to by the large number and variety of patents and solutions, the prior art has not yet developed a satisfactory solution which will enable the preparation of an anti-caking nitrogen-containing material that will yield the desired percent by weight nitrogen upon analysis; yet will flow freely, will resist caking on long term storage, is simple enough and employs an economical enough additive not to be prohibitively costly.